Manuel Pellegrini's tenure as manager of Manchester City opened with a 2-0 defeat by SuperSport United on the club's pre-season tour of South Africa on Sunday.

The Senegalese striker Mame Niang and the South African international Kermit Erasmus scored second-half goals for SuperSport at Loftus Versfeld to beat a City team that were clearly in pre-season mode and far from top gear.

Pellegrini shrugged off the defeat, saying City had started proper pre-season preparations only last week.

"I think it's always important to win but it's not the most important thing at the moment," Pellegrini said. "We are very far [from top form]. We've just had our first week. When pre-season continues, after three weeks or a month, we will see where we are."

Edin Dzeko and James Milner went closest to scoring for City, while Pellegrini fielded completely different line-ups in each half. The Brazil midfielder Fernandinho started for City in a subdued debut alongside the young Spanish midfielder Denis Suárez. Both made way as part of the wholesale changes for the second half.

Niang rose between Joleon Lescott and Matija Nastasic to head past the reserve goalkeeper Costel Pantilimon for the opener in the 56th minute. Erasmus ran on to a defence-splitting pass to flick the ball past Pantilimon and into the far right corner for the second in the 82nd minute.

Dzeko had combined with Samir Nasri to force a double save from Ronwen Williams in the opening 20 minutes and Milner was denied by a combination of the substitute keeper Boalefa Phule – one of SuperSport's host of changes – and a diving block by a defender in the 73rd minute.

Joe Hart, Vincent Kompany, Fernandinho, Nasri and Dzeko all went off at half-time, with Lescott and Nastasic coming on and Yaya Touré taking over as captain.

Touré had a speculative long-range shot in the 76th minute that sailed over the crossbar before he limped off at the end.

City's players unveiled a shirt dedicated to the former South African president Nelson Mandela before kick-off. The Premier League visitors will play their second game on tour on Thursday to mark his 95th birthday.